Here's one way to operate and bias a THAT1646 for single supply operation:
Image courtesy of THAT Corporation
If the input is at or near the same DC potential as Vref (the one-half Vcc potential at the output of U2A) then C2 and R1 may be elimanted and the input direct coupled.
R3 and C4 minimize the series inductance "seen" by pin 3 of the THAT 1646 to prevent oscillation.
The MC33178 is an ideal low-cost, relatively low power, and low noise rail splitter. C1 and C3 may be sized based upon the expected load impedance.
For multiple 1646s using a shared rail splitter providing 1/2 Vcc Vref:
Image courtesy of THAT Corporation
THAT1646 Operation From A Single Supply Voltage
- mediatechnology
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Re: THAT1646 Operation From A Single Supply Voltage
Is there perhaps an error in the first image?
The first image shows R2 & C4 in series acting as a snubber, while U2A feeds pin 3 directly.
I suppose if output from U2A is close enough and the opamp output impedance at HF is reasonably low this should work, but I am not so sure what R2 + C4 does here.
The second image shows the virtual ground being fed to pin 3 via a 47R isolation resistor, while C2 decouples pin 3 to the negative supply.
From my limited electronics knowledge I am guessing that R2 & C4 values are rather empirical, and I should be fine substituting other small caps and resistors in there place, or am I totally off? I am thinking of 120R, 100nF ceramic disc or 220nF MKTs I have laying around.
The first image shows R2 & C4 in series acting as a snubber, while U2A feeds pin 3 directly.
I suppose if output from U2A is close enough and the opamp output impedance at HF is reasonably low this should work, but I am not so sure what R2 + C4 does here.
The second image shows the virtual ground being fed to pin 3 via a 47R isolation resistor, while C2 decouples pin 3 to the negative supply.
From my limited electronics knowledge I am guessing that R2 & C4 values are rather empirical, and I should be fine substituting other small caps and resistors in there place, or am I totally off? I am thinking of 120R, 100nF ceramic disc or 220nF MKTs I have laying around.
Re: THAT1646 Operation From A Single Supply Voltage
I'm sure Wayne will drop in and tell you from the horse's mouth, but it is not unusual to shunt across an opamp output like that to insure a low impedance at very high frequency where cheap opamps run out of gain bandwidth.
The 1646 is a wide band part, and I wouldn't assume their app notes to be wrong. While there is nothing wrong with asking.
JR
The 1646 is a wide band part, and I wouldn't assume their app notes to be wrong. While there is nothing wrong with asking.
JR
Cancel the "cancel culture", do not support mob hatred.
Re: THAT1646 Operation From A Single Supply Voltage
Actually I have only DRV134 to play around with, but I remember reading here that they are principally the same.
Anyhow, I'd love to hear more about these things!
Anyhow, I'd love to hear more about these things!
- mediatechnology
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Re: THAT1646 Operation From A Single Supply Voltage
nereis - Sorry been AWOL.
Both figures are correct though different in the location of the series resistor.
It's been about 5 years since I did both. I need to go back and look at my notes.
I seem to recall that in the first figure connecting the op amp output directly to pin 3 allowed <<47R impedance at LF to realize maximum output balance in the OutSmarts bridge.
With multiple 1646s sharing a bus, in the second figure, this wasn't practical.
Bottom line is that it doesn't take much capacitance at pin 3 of the 1646 to reduce the output "inductance" (rising impedance vs frequency) of the op amp.
The DRV134 may not require the capacitance.
Both figures are correct though different in the location of the series resistor.
It's been about 5 years since I did both. I need to go back and look at my notes.
I seem to recall that in the first figure connecting the op amp output directly to pin 3 allowed <<47R impedance at LF to realize maximum output balance in the OutSmarts bridge.
With multiple 1646s sharing a bus, in the second figure, this wasn't practical.
Bottom line is that it doesn't take much capacitance at pin 3 of the 1646 to reduce the output "inductance" (rising impedance vs frequency) of the op amp.
The DRV134 may not require the capacitance.
Re: THAT1646 Operation From A Single Supply Voltage
Thanks for the info, I think I'll still stick a small cap in there just to make sure it works.
I contemplated over using TLE2426 as rail splitter until I saw the Output Impedance vs Frequency plot in the datasheet, the rise starting at 200hz looks quite bad compared to most opamps.
I contemplated over using TLE2426 as rail splitter until I saw the Output Impedance vs Frequency plot in the datasheet, the rise starting at 200hz looks quite bad compared to most opamps.
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Re: THAT1646 Operation From A Single Supply Voltage
I think it may be a little noisy too. IIRC that's why I didn't use the TLE2426.
The MC33178, considering it's low power, had pretty decent performer as a rail splitter and LP audio op amp.
A 5534 works well but has considerable Icc compared to the 33178.
The MC33178, considering it's low power, had pretty decent performer as a rail splitter and LP audio op amp.
A 5534 works well but has considerable Icc compared to the 33178.